Contact structures in semiconductor devices

ABSTRACT

A semiconductor device with different configurations of contact structures and a method of fabricating the same are disclosed. The semiconductor device includes first and second gate structures disposed on first and second fin structures, first and second source/drain (S/D) regions disposed on the first and second fin structures, first and second contact structures disposed on the first and second S/D regions, and a dipole layer disposed at an interface between the first nWFM silicide layer and the first S/D region. The first contact structure includes a first nWFM silicide layer disposed on the first S/D region and a first contact plug disposed on the first nWFM silicide layer. The second contact structure includes a pWFM silicide layer disposed on the second S/D region, a second nWFM silicide layer disposed on the pWFM silicide layer, and a second contact plug disposed on the pWFM silicide layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 63/062,821, titled “Semiconductor Structure and Methodfor Manufacturing the Same,” filed Aug. 7, 2020, the disclosure of whichis incorporated by reference herein in its entirety.

BACKGROUND

With advances in semiconductor technology, there has been increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices, such as metal oxide semiconductor field effect transistors(MOSFETs), including planar MOSFETs and fin field effect transistors(finFETs). Such scaling down has increased the complexity ofsemiconductor manufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures.

FIG. 1 illustrates an isometric view of a semiconductor device, inaccordance with some embodiments.

FIGS. 2A-2D, 3A-3D, 4A-4D, and 5A-5D illustrate cross-sectional views ofa semiconductor device with different contact structures, in accordancewith some embodiments.

FIGS. 2E-2F and 3E illustrate device characteristics of a semiconductordevice with different contact structures, in accordance with someembodiments.

FIG. 6 is a flow diagram of a method for fabricating a semiconductordevice with different contact structures, in accordance with someembodiments.

FIGS. 7A-23D illustrate cross-sectional views of a semiconductor devicewith different contact structures at various stages of its fabricationprocess, in accordance with some embodiments.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the processfor forming a first feature over a second feature in the descriptionthat follows may include embodiments in which the first and secondfeatures are formed in direct contact, and may also include embodimentsin which additional features may be formed between the first and secondfeatures, such that the first and second features may not be in directcontact. As used herein, the formation of a first feature on a secondfeature means the first feature is formed in direct contact with thesecond feature. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “exemplary,” etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of theteachings herein.

In some embodiments, the terms “about” and “substantially” can indicatea value of a given quantity that varies within 5% of the value (e.g.,±1%, ±2%, ±3%, ±4%, ±5% of the value). These values are merely examplesand are not intended to be limiting. The terms “about” and“substantially” can refer to a percentage of the values as interpretedby those skilled in relevant art(s) in light of the teachings herein.

The fin structures disclosed herein may be patterned by any suitablemethod. For example, the fin structures may be patterned using one ormore photolithography processes, including double-patterning ormulti-patterning processes. Double-patterning or multi-patterningprocesses can combine photolithography and self-aligned processes,allowing patterns to be created that have, for example, pitches smallerthan what is otherwise obtainable using a single, directphotolithography process. For example, a sacrificial layer is formedover a substrate and patterned using a photolithography process. Spacersare formed alongside the patterned sacrificial layer using aself-aligned process. The sacrificial layer is then removed, and theremaining spacers may then be used to pattern the fin structures.

The present disclosure provides example semiconductor devices with FETs(e.g., finFETs) having source/drain (S/D) contact structures differentfrom each other and provides example methods of forming such FETs on thesame substrate with reduced contact resistance between S/D regions andS/D contact structures. The example method forms arrays of n- and p-typeS/D regions on fin structures of n-type FETs (NFETs) and p-type FETs(PFETs), respectively, of the semiconductor device. In some embodiments,S/D contact structures on n-type S/D regions have silicide layersdifferent from silicide layers of p-type S/D contact structures onp-type S/D regions.

The contact resistances between the S/D regions and the S/D contactstructures are directly proportional to the Schottky barrier heights(SBHs) between the materials of the S/D regions and the silicide layersof the S/D contact structures. For n-type S/D regions, reducing thedifference between the work function value of the silicide layers andthe conduction band energy of the n-type material of the S/D regions canreduce the SBH between the n-type S/D regions and the S/D contactstructures. In contrast, for p-type S/D regions, reducing the differencebetween the work function value of the silicide layers and the valenceband energy of the p-type material of the S/D regions can reduce the SBHbetween the p-type S/D regions and the S/D contact structures. In someembodiments, since the S/D regions of NFETs and PFETs are formed withrespective n-type and p-type materials, the S/D contact structures ofNFETs and PFETs are formed with silicide layers different from eachother to reduce the contact resistances between the S/D contactstructures and the different materials of the S/D regions.

In some embodiments, the NFET S/D contact structures are formed withn-type work function metal (nWFM) silicide layers (e.g., titaniumsilicide) that have a work function value closer to a conduction bandenergy than a valence band energy of the n-type S/D regions. Incontrast, the PFET S/D contact structures are formed with p-type WFM(pWFM) silicide layers (e.g., nickel silicide or cobalt silicide) thathave a work function value closer to a valence band energy than aconduction band energy of the p-type S/D regions. The nWFM silicidelayers can be formed from a silicidation reaction between the n-type S/Dregions and an nWFM layer disposed on the n-type S/D regions. The pWFMsilicide layers can be formed from a silicidation reaction between thep-type S/D regions and a pWFM layer disposed on the p-type S/D regions.

In some embodiments, dipole layers can be formed at interfaces betweenthe S/D regions and the silicide layers of NFETs to further reduce theSBHs between the n-type S/D regions and the S/D contact structures. Thedipole layers can be formed by doping the silicide layers with metalshaving electronegativity values lower than the metals of the silicidelayers. The metal dopants can induce the formation of dipoles betweenthe metal dopants and the semiconductor elements of the n-type S/Dregions. Such selective formation of silicide layers in NFETs and PFETscan reduce the contact resistances of the semiconductor devices by about50% to about 70% compared to NFETs and PFETs with similar silicidelayers, and consequently improve the performance of the semiconductordevices.

FIG. 1 illustrates an isometric view of a semiconductor device 100 withNFET 102N and PFET 102P, according to some embodiments. NFET 102N andPFET 102P can have different cross-sectional views, as illustrated inFIGS. 2A-2D, 3A-3D, 4A-4D, and 5A-5D, according to various embodiments.FIGS. 2A-5A and 2C-5C illustrate cross-sectional views of NFET 102Nalong respective lines A-A and C-C of FIG. 1. FIGS. 2B-5B and 2D-5Dillustrate cross-sectional views of PFET 102P along respective lines B-Band D-D of FIG. 1. FIGS. 2A-2D, 3A-3D, 4A-4D, and 5A-5D illustratecross-sectional views of semiconductor device 100 with additionalstructures that are not shown in FIG. 1 for simplicity. The discussionof elements of NFET 102N and PFET 102P with the same annotations appliesto each other, unless mentioned otherwise.

Referring to FIG. 1, NFET 102N can include an array of gate structures112N disposed on fin structure 106N, and PFET 102P can include an arrayof gate structures 112P disposed on fin structure 106P. NFET 102N canfurther include an array of S/D regions 108N (one of S/D regions 108Nvisible in FIG. 1) disposed on portions of fin structure 106N that arenot covered by gate structures 112N. Similarly, PFET 102P can furtherinclude an array of epitaxial S/D regions 108P (one of S/D regions 108Pvisible in FIG. 1) disposed on portions of fin structure 106P that arenot covered by gate structures 112P.

Semiconductor device 100 can further include gate spacers 114, shallowtrench isolation (STI) regions 116, etch stop layer (ESL) 117, andinterlayer dielectric (ILD) layers 118A-118B (ILD layer 118B not shownin FIG. 1 for simplicity; shown in FIGS. 2A-2D, 3A-3D, 4A-4D, and5A-5D). ILD layer 118A can be disposed on ESL 117. ESL 117 can beconfigured to protect gate structures 112N and 112P and/or S/D regions108N and 108P. In some embodiments, gate spacers 114, STI regions 116,ESL 117, and ILD layers 118A-118B can include an insulating material,such as silicon oxide, silicon nitride (SiN), silicon carbon nitride(SiCN), silicon oxycarbon nitride (SiOCN), and silicon germanium oxide.In some embodiments, gate spacers 114 can have a thickness of about 2 nmto about 9 nm for adequate electrical isolation of gate structures 112Nand 112P from adjacent structures.

Semiconductor device 100 can be formed on a substrate 104 with NFET 102Nand PFET 102P formed on different regions of substrate 104. There may beother FETs and/or structures (e.g., isolation structures) formed betweenNFET 102N and PFET 102P on substrate 104. Substrate 104 can be asemiconductor material, such as silicon, germanium (Ge), silicongermanium (SiGe), a silicon-on-insulator (SOI) structure, and acombination thereof. Further, substrate 104 can be doped with p-typedopants (e.g., boron, indium, aluminum, or gallium) or n-type dopants(e.g., phosphorus or arsenic). In some embodiments, fin structures106N-106P can include a material similar to substrate 104 and extendalong an X-axis.

Referring to FIGS. 2A-2D, NFET-PFET 102N-102P can include gatestructures 112N-112P, S/D regions 108N-108P, and S/D contact structures120N-120P disposed on S/D regions 108N-108P. Gate structures 112N-112Pcan be multi-layered structures. Each of gate structures 112N-112P caninclude an interfacial oxide (IO) layer 122, a high-k (HK) gatedielectric layer 124 disposed on IO layer 122, a work function metal(WFM) layer 126 disposed on HK gate dielectric layer 124, a gate metalfill layer 128 disposed on WFM layer 126, and a gate capping layer 130disposed on HK gate dielectric layer 124, WFM layer 126, and gate metalfill layer 128.

IO layers 122 can include silicon oxide (SiO₂), silicon germanium oxide(SiGeO_(x)), or germanium oxide (GeO_(x)). HK gate dielectric layers 124can include a high-k dielectric material, such as hafnium oxide (HfO₂),titanium oxide (TiO₂), hafnium zirconium oxide (HfZrO), tantalum oxide(Ta₂O₃), hafnium silicate (HfSiO₄), zirconium oxide (ZrO₂), andzirconium silicate (ZrSiO₂). WFM layers 126 of gate structures 112N caninclude titanium aluminum (TiAl), titanium aluminum carbide (TiAlC),tantalum aluminum (TaAl), tantalum aluminum carbide (TaAlC), Al-dopedTi, Al-doped TiN, Al-doped Ta, Al-doped TaN, a combination thereof, orother suitable Al-based materials. WFM layers 126 of gate structures112P can include substantially Al-free (e.g., with no Al) Ti-based orTa-based nitrides or alloys, such as titanium nitride (TiN), titaniumsilicon nitride (TiSiN), titanium gold (Ti—Au) alloy, titanium copper(Ti—Cu) alloy, tantalum nitride (TaN), tantalum silicon nitride (TaSiN),tantalum gold (Ta—Au) alloy, tantalum copper (Ta—Cu), and a combinationthereof. Gate metal fill layers 128 can include a suitable conductivematerial, such as tungsten (W), Ti, silver (Ag), ruthenium (Ru),molybdenum (Mo), copper (Cu), cobalt (Co), Al, iridium (Ir), nickel(Ni), metal alloys, and a combination thereof. In some embodiments, gatestructures 112N-112P can be electrically isolated from overlyinginterconnect structures (not shown) by gate capping layers 130, whichcan include nitride layers.

Each of S/D regions 108N can include a stack of epitaxial layers—alightly doped (LD) n-type layer 109N epitaxially grown on fin structure106N, a heavily doped (HD) n-type layer 110N epitaxially grown on LDn-type layer 109N, and a p-type capping layer 111N epitaxially grown onHD n-type layer 110N. In some embodiments, LD and HD n-type layers109N-110N can include epitaxially-grown semiconductor material, such assilicon, and n-type dopants, such as phosphorus and other suitablen-type dopants. LD n-type layers 109N can include a doping concentrationranging from about 10¹⁵ atoms/cm³ to about 10¹⁸ atoms/cm³, which islower than a doping concentration of HD n-type layers 110N, which canrange from about 10¹⁹ atoms/cm³ to about 10²³ atoms/cm³. In someembodiments, HD n-type layer 110N is thicker than LD n-type layer 109N.

Similarly, each of S/D regions 108P can include a stack of epitaxiallayers—a LD p-type layer 109P epitaxially grown on fin structure 106P, aHD p-type layer 110P epitaxially grown on LD p-type layer 109P, and ann-type capping layer 111P epitaxially grown on HD p-type layer 110P. Insome embodiments, LD and HD p-type layers 109P-110P can includeepitaxially-grown semiconductor material, such as SiGe, and p-typedopants, such as boron and other suitable p-type dopants. LD p-typelayers 109P can include a doping concentration ranging from about 10¹⁵atoms/cm³ to about 10¹⁸ atoms/cm³, which is lower than a dopingconcentration of HD p-type layers 110P, which can range from about 10¹⁹atoms/cm³ to about 10²³ atoms/cm³. In some embodiments, LD p-type layers109P can include a Ge concentration ranging from about 5 atomic percentto about 45 atomic percent, which is lower than a Ge concentration of HDp-type layers 110P, which can range from about 50 atomic percent toabout 80 atomic percent. In some embodiments, HD p-type layer 110P isthicker than LD p-type layer 109P.

P-type capping layers 111N include a material and dopants similar to HDp-type layers 110P and n-type capping layers 111P include a material anddopants similar to HD n-type layers 110N. In some embodiments, p- andn-type capping layers 111N-111P can include doping concentrationsranging from about 10¹⁹ atoms/cm³ to about 10²³ atoms/cm³. P- and n-typecapping layers 111N-111P are referred to as reverse capping layers111N-111P because these layers are disposed on oppositely conductive HDn- and p-type layers 110N-110P, respectively. These reverse cappinglayers 111N-111P are used in the selective formation of silicide layers131 and 132N in respective S/D regions 108P and 108N, which aredescribed in detail below. In some embodiments, the thicknesses of p-and n-type capping layers 111N-111P along a Z-axis can range from about1 nm to about 3 nm. The thicknesses below this range may not form acontinuous layer, and may be inadequate for the selective formation ofsilicide layers 131 and 132N. On the other hand, if the thicknesses areabove this range, the processing time (e.g., epitaxial growth time)increases, and consequently increase device manufacturing cost.

Referring to FIGS. 2A and 2C, S/D contact structure 120N is disposed onS/D region 108N. In some embodiments, S/D contact structure 120N caninclude (i) an nWFM silicide layer 132N disposed on HD n-type layer110N, (ii) a contact plug 134N disposed on nWFM silicide layer 132N,(iii) a stack of metal-based liners 135N disposed on sidewalls ofcontact plug 134N, and (iv) a barrier layer 142N disposed on stack ofmetal-based liners 135N. NFET 102N can further include a dipole layer144 at an interface (“interface 132N-110N”) between nWFM silicide layer132N and HD n-type layer 110N. In some embodiments, interface 132N-110Ncan be within S/D region 108N and below top surface of S/D region 108N.

In some embodiments, top surface of nWFM silicide layer 132N can beabove top surface of S/D region 108N (shown in FIGS. 2A and 2C) or canbe substantially coplanar with top surface of S/D region 108N (notshown). In some embodiments, nWFM silicide layer 132N can form angles Aand B with the stack of metal-based liners 135N, as shown in FIG. 2C.Angles A and B can be similar or different from each other and can rangefrom about 45 degrees to about 60 degrees. In some embodiments, nWFMsilicide layer 132N can include a metal or a metal silicide with a workfunction value closer to a conduction band-edge energy than a valenceband-edge energy of the material of HD n-type layer 110N. For example,the metal or the metal silicide can have a work function value less than4.5 eV (e.g., about 3.5 eV to about 4.4 eV), which can be closer to theconduction band energy (e.g., 4.1 eV of Si or 3.8 eV of SiGe) than thevalence band energy (e.g., 5.2 eV of Si or 4.8 eV of SiGe) of Si-basedor SiGe-based material of HD n-type layer 110N. In some embodiments, themetal silicide of nWFM silicide layer 132N can include titanium silicide(Ti_(x)Si_(y)), tantalum silicide (Ta_(x)Si_(y)), molybdenum silicide(Mo_(x)Si_(y)), zirconium silicide (Zr_(x)Si_(y)), hafnium silicide(Hf_(x)Si_(y)), scandium silicide (Sc_(x)Si_(y)), yttrium silicide(Y_(x)Si_(y)), terbium silicide (Tb_(x)Si_(y)), lutetium silicide(Lu_(x)Si_(y)), erbium silicide (Er_(x)Si_(y)), ybtterbium silicide(Yb_(x)Si_(y)), europium silicide (Eu_(x)Si_(y)), thorium silicide(Th_(x)Si_(y)), or a combination thereof.

In some embodiments, nWFM silicide layer 132N can further includedopants of a transition metal, which has an electronegativity valuesmaller than the electronegativity value of the metal of the metalsilicide included in nWFM silicide layer 132N. For example, dopants caninclude a transition metal, such as zirconium (Zr), hafnium (Hf),ybtterbium (Yb), yttrium (Y), erbium (Er), cerium (Ce), scandium (Sc),and a combination thereof. In some embodiments, some dopants can diffuseinto HD n-type layer 110N. The dopants can induce the formation ofcharged dipoles in dipole layer 144 at interface 132N-110N. Dipole layer144 can include charged dipoles of silicon ions from HD n-type layer110N and transition metal ions from the dopants in nWFM silicide layer132N. For example, dipole layer 144 can include Zr—Si, Hf—Si, Yb—Si,Y—Si, Er—Si, Ce—Si, or Sc—Si dipoles when nWFM silicide layer 132Nincludes Zr, Hf, Yb, Y, Er, Ce, or Sc dopants, respectively.

The electric fields generated at interface 132N-110N by dipoles indipole layer 144 can reduce the SBH between nWFM silicide layer 132N andHD n-type layer 110N, and consequently reduce the contact resistancebetween S/D contact structure 120N and S/D region 108N. Based on thetype and concentration of dipoles in dipole layer 144 at interface132N-110N, the SBH between nWFM silicide layer 132N and HD n-type layer110N can be reduced by about 35% to about 70% compared to the SBHbetween nWFM silicide layer 132N and HD n-type layer 110N without dipolelayer 144. The concentration of dipoles at interface 132N-110N isdirectly proportional to the concentration of dopants in nWFM silicidelayer 132N and/or interface 132N-110N. The concentration of dopants innWFM silicide layer 132N and/or interface 132N-110N can range from about1 atomic percent to about 10 atomic percent. The dopant concentrationbelow this range may not induce the formation of dipoles in dipole layer144. On the other hand, if the dopant concentration is above this range,the duration and complexity of the doping process increases, andconsequently increase device manufacturing cost.

The dopant concentration can have profiles 246, 248, and/or 250 acrossnWFM silicide layer 132N and HD n-type layer 110N along lines E-E ofFIGS. 2A and 2C, as shown in FIG. 2E, according to various embodiments.The dopant concentration can have profile 246 with a peak dopantconcentration C1 at interface 132N-110N when nWFM silicide layer 132N isdoped with a transition metal (e.g., Zr, Hf, etc.) in a doping processthat does not include a high temperature (e.g., temperature greater than500° C.) annealing process, as described in detail below. The dopantconcentration can have profile 248 when nWFM silicide layer 132N isdoped with a non-Zr-based transition metal (e.g., Hf, Ce, Er, etc.) in adoping process that does not include a high temperature annealingprocess. The non-Zr-based transition dopants can have a lowerthermodynamic stability at interface 132N-110N than Zr dopants, whichcan cause a larger number of the non-Zr-based transition dopants todiffuse away from interface 132N-110N and into nWFM silicide layer 132N.As a result, as shown in FIG. 2E, the peak dopant concentration ofprofile 248 can be a distance D1 (e.g., about 0.1 nm to about 0.5 nm)away from interface 132N-110N and can have a dopant concentration C2 atinterface 132N-110N, which is smaller than peak dopant concentration C1.

In some embodiments, when the doping of nWFM silicide layer 132Nincludes a high temperature annealing process, the non-Zr-based dopantscan diffuse further into nWFM silicide layer 132N due to their lowerthermodynamic stability at interface 132N-110N and can have a dopantconcentration profile 250, as shown in FIG. 2E. The peak dopantconcentration of profile 250 can be a distance D2 (e.g., about 0.2 nm toabout 0.8 nm) away from interface 132N-110N, which is greater thandistance D1, and can have a dopant concentration C3 at interface132N-110N, which is smaller than dopant concentration C2. As theconcentration of dopants at interface 132N-110N is directly proportionalto the concentration of dipoles at interface 132N-110N, dipoleconcentration in dipole layer 144 can be greater for profile 246 thanfor profiles 248 and 250, and dipole concentration in dipole layer 144for profile 248 can be greater than for profile 250. As a result, theSBH between nWFM silicide layer 132N and HD n-type layer 110N can belower for profile 246 than for profiles 248 and 250, and the SBH betweennWFM silicide layer 132N and HD n-type layer 110N can be lower forprofile 248 than for profile 250. In some embodiments, dopantconcentration across along lines E-E of FIGS. 2A and 2C can haveprofiles 246 and 248 or can have profiles 246 and 250 when nWFM silicidelayer 132N is doped with a combination of Zr metal and one or morenon-Zr-based transition metals.

Referring back to FIGS. 2A and 2C, contact plug 134N can includeconductive materials, such as cobalt (Co), tungsten (W), ruthenium (Ru),iridium (Ir), nickel (Ni), osmium (Os), rhodium (Rh), aluminum (Al),molybdenum (Mo), copper (Cu), zirconium (Zr), stannum (Sn), silver (Ag),gold (Au), zinc (Zn), cadmium (Cd), and a combination thereof. In someembodiments, stack of metal-based liners 135N can include a first liner136N, a second liner 138N, and a third liner 140N. First liner 136N canbe a portion of a source layer that is used in the formation of nWFMsilicide layer 132N, as described in detail below, and can include ametal of nWFM silicide layer 132N or can include an oxide of a metal ofnWFM silicide layer 132N. Second liner 138N can be a portion of a sourcethat is used in the doping of nWFM silicide layer 132N, as described indetail below, and can include a transition metal of the dopants in nWFMsilicide layer 132N or can include an oxide of the metal of the dopants.Third liner 140N can be a portion of a source layer that is used in theformation of pWFM silicide layer 132P, as described in detail below, andcan include a metal of pWFM silicide layer 132P or can include an oxideof a metal of pWFM silicide layer 132P. In some embodiments, secondand/or third liners 138N-140N may not be present in stack of metal-basedliners 135N or stack of metal-based liners 135N may not be present inS/D contact structure 120N (shown in FIGS. 23A and 23C). Barrier layer142N can include a nitride material and can reduce or prevent thediffusion of oxygen atoms from ILD layers 118A-118B into contact plug134N to prevent the oxidation of the conductive material of contact plug134N.

Referring to FIGS. 2B and 2D, S/D contact structure 120P is disposed onS/D region 108P. In some embodiments, S/D contact structure 120P caninclude (i) an pWFM silicide layer 131 disposed on HD p-type layer 110P,(ii) an nWFM silicide layer 132P disposed on pWFM silicide layer 131,(iii) a contact plug 134P disposed on nWFM silicide layer 132P, (iv) astack of metal-based liners 135P with first, second, and third liners136P, 138P, and 140P disposed on sidewalls of contact plug 134P, and (v)a barrier layer 142P disposed on stack of metal-based liners 135P. Thediscussion of contact plug 134N, barrier layer 142N, stack ofmetal-based liners 135N with first, second, and third liners 136N-140Napplies to contact plug 134P, barrier layer 142P, and stack ofmetal-based liners 135P with first, second, and third liners 136P-140P,respectively, unless mentioned otherwise. In some embodiments, secondand/or third liners 138P-140P may not be present in stack of metal-basedliners 135P or stack of metal-based liners 135P may not be present inS/D contact structure 120P (shown in FIGS. 23B and 23D).

In some embodiments, top surface of pWFM silicide layer 131 can be abovetop surface of S/D region 108P (shown in FIGS. 2B and 2D) or can besubstantially coplanar with top surface of S/D region 108P (not shown).In some embodiments, pWFM silicide layer 131 can form angles C and Dwith the stack of metal-based liners 135P, as shown in FIG. 2D. Angles Cand D can be similar or different from each other and can range fromabout 45 degrees to about 60 degrees. In some embodiments, pWFM silicidelayer 131 can include a metal or a metal silicide with a work functionvalue closer to a valence band-edge energy than a conduction band-edgeenergy of the material of HD p-type layer 110P. For example, the metalor the metal silicide can have a work function value greater than 4.5 eV(e.g., about 4.5 eV to about 5.5 eV), which can be closer to the valenceband energy (e.g., 5.2 eV of Si or 4.8 eV of SiGe) than the conductionband energy (e.g., 4.1 eV of Si or 3.8 eV of SiGe) of Si-based orSiGe-based material of HD p-type layer 110P. In some embodiments, themetal silicide of pWFM silicide layer 131 can include nickel silicide(Ni_(x)Si_(y)), cobalt silicide (Co_(x)Si_(y)), manganese silicide(Mn_(x)Si_(y)), tungsten silicide (W_(x)Si_(y)), iron silicide(Fe_(x)Si_(y)), rhodium silicide (Rh_(x)Si_(y)), palladium silicide(Pd_(x)Si_(y)), ruthenium silicide (Ru_(x)Si_(y)), platinum silicide(Pt_(x)Si_(y)), iridium silicide (Ir_(x)Si_(y)), osmium silicide(Os_(x)Si_(y)), or a combination thereof.

The metal silicide of pWFM silicide layer 131 is different from themetal silicide of nWFM layers 132N-132P and can have a work functionvalue greater than the work function values of nWFM silicide layers132N-132P. In some embodiments, nWFM silicide layer 132P can be formedat the same time as nWFM silicide layer 132N and can include a metalsilicide and dopants similar to nWFM silicide layer 132N. Some of thedopants may diffuse into pWFM silicide layer 132. Similar to dopantconcentration profiles 246-250, the dopant concentration across nWFMsilicide layer 132P and pWFM silicide layer 131 can have profiles 252,254, and/or 256 along lines F-F of FIGS. 2B and 2D, as shown in FIG. 2F,according to various embodiments. The dopant concentration can haveprofile 252 with a peak dopant concentration C4 at an interface(“interface 131-132P”) between pWFM silicide layer 131 and nWFM silicidelayer 132P when nWFM silicide layer 132P is doped with a transitionmetal (e.g., Zr, Hf, etc.) in a doping process that does not include ahigh temperature annealing process. The dopant concentration can haveprofile 254 when nWFM silicide layer 132P is doped with a non-Zr-basedtransition metal (e.g., Hf, Ce, Er, etc.) in a doping process that doesnot include a high temperature annealing process. The peak dopantconcentration of profile 254 can be a distance D3 (e.g., about 0.1 nm toabout 0.5 nm) away from interface 131-132P and can have a dopantconcentration C5 at interface 131-132P , which is smaller than peakdopant concentration C4.

The dopant concentration can have profile 256 when nWFM silicide layer132P is doped with a non-Zr-based transition metal (e.g., Hf, Ce, Er,etc.) in a doping process that includes a high temperature annealingprocess. The peak dopant concentration of profile 256 can be a distanceD4 (e.g., about 0.2 nm to about 0.8 nm) away from interface 131-132P,which is greater than distance D3, and can have a dopant concentrationC6 at interface 131-132P, which is smaller than dopant concentration C5.In some embodiments, dopant concentration across along lines F-F ofFIGS. 2B and 2D can have profiles 252 and 254 or can have profiles 252and 256 when nWFM silicide layer 132P is doped with a combination of Zrmetal and one or more non-Zr-based transition metals. In someembodiments, unlike nWFM silicide layer 132N, nWFM silicide layer 132Pcan be undoped. For effective reduction of contact resistance, thethickness of pWFM silicide layer 131 along a Z-axis can range from about1 nm to about 3 nm and the thicknesses of nWFM silicide layers 132N-132Palong a Z-axis can range from about 2 nm to about 6 nm.

In some embodiments, S/D contact structures 120N-120P can havecross-sectional views as shown in FIGS. 3A-3D when nWFM silicide layers132N-132P are doped with Zr metal in a doping process that includes ahigh temperature annealing process. Referring to FIGS. 3A and 3C, S/Dcontact structure 120N can include a Zr-based ternary compound (ZTC)layer 133 interposed between nWFM silicide layer 132N and HD n-typelayer 110N. The Zr dopants of nWFM silicide layer 132N can interact withSi atoms of HD n-type layer 110N and metal atoms of nWFM silicide layer132N during the high temperature annealing process to form ZTC layer133. In some embodiments, ZTC layer 133 can include zirconium titaniumsilicide (Zr₃Ti₂Si₃) when nWFM silicide layer 132N includesTi_(x)Si_(y). ZTC layer 133 can induce the formation of dipole layer 145at an interface (“interface 133-110N”) between ZTC layer 133 and HDn-type layer 110N. In some embodiments, interface 133-110N can be withinS/D region 108N and below top surface of S/D region 108N. Dipole layer145 can include Zr—Si dipoles of Zr metal ions from ZTC layer 133 andsilicon ions from HD n-type layer 110N.

Similar to dipole layer 144, the electric fields generated at interface133-110N by dipole layer 145 can reduce the SBH by about 35% to about70% between nWFM silicide layer 132N and HD n-type layer 110N, andconsequently reduce the contact resistance between S/D contact structure120N and S/D region 108N. The concentration of Zr atoms in ZTC layer 133can range from about 1 atomic percent to about 10 atomic percent. Insome embodiments, the Zr atoms can have a concentration profile 358across nWFM silicide layer 132N, ZTC layer 133, and HD n-type layer 110Nalong lines G-G of FIGS. 3A and 3C, as shown in FIG. 3E.

Referring to FIGS. 3B and 3D, the Zr dopants of nWFM silicide layer 132Pdoes not form a ZTC layer in S/D contact structure 120P during the hightemperature annealing process due to the interposing pWFM silicide layer131 that can prevent Zr dopants from interacting with Si atoms of HDp-type layer 110P. The Zr dopants can have a concentration profilesimilar to profile 252 of FIG. 2F.

In some embodiments, S/D contact structures 120N-120P can includerespective nitride capping layers 146N-146P, as shown in FIGS. 4A-4D.Nitride capping layers 146N-146P can be formed to protect the underlyinglayers (e.g., silicide layers 131 and 132N-132P) during subsequentprocessing of S/D contact structures 120N-120P.

In some embodiments, instead of interface 132N-110N being substantiallycoplanar with the interface (“interface 111N-110N”) between p-typecapping layer 111N and HD n-type layer 110N, as shown in FIGS. 2A-4A and2C-4C, interface 132N-110N can be non-coplanar with interface 111N-110N,as shown in FIGS. 5A and 5C. The non-coplanarity can occur when thesilicon of p-type capping layer 111N is not used in the formation ofnWFM silicide layer 132N. Instead, the silicon of HD n-type layer 110Nis consumed during the formation of nWFM silicide layer 132N, and as aresult, nWFM silicide layer 132N extends into HD n-type layer 110. Theformation of nWFM silicide layer 132 with and without p-type cappinglayer 111N is described in detail below. The interface between pWFMsilicide layer 131 and HD p-type layer 110N can be substantiallycoplanar with the interface between n-type capping layer 111P and HDp-type layer 110P, as shown in FIGS. 2B-5B and 2D-5D.

FIG. 6 is a flow diagram of an example method 600 for fabricating NFET102N and PFET 102P of semiconductor device 100, according to someembodiments. For illustrative purposes, the operations illustrated inFIG. 6 will be described with reference to the example fabricationprocess for fabricating NFET 102N and PFET 102P as illustrated in FIGS.7A-23D. FIGS. 7A-23A and 7C-23C are cross-sectional views of NFET 102Nalong respective lines A-A and C-C of FIG. 1 and FIGS. 7B-23B and 7D-23Dare cross-sectional views of PFET 102P along respective lines B-B andD-D of FIG. 1 at various stages of fabrication, according to someembodiments. Operations can be performed in a different order or notperformed depending on specific applications. It should be noted thatmethod 600 may not produce a complete NFET 102N and PFET 102P.Accordingly, it is understood that additional processes can be providedbefore, during, and after method 600, and that some other processes mayonly be briefly described herein. Elements in FIGS. 7A-23D with the sameannotations as elements in FIGS. 1 and 2A-5D are described above.

In operation 605, polysilicon structures and n- and p-type S/D regionsare formed on fin structures on a substrate. For example, as shown inFIGS. 7A-7B, polysilicon structures 712N-712P and S/D regions 108N-108Pare formed on fin structures 106N-106P, which are formed on substrate104. During subsequent processing, polysilicon structures 712N-712P canbe replaced in a gate replacement process to form gate structures112N-112P. In some embodiments, the formation of S/D regions 108N-108Pcan include sequential operations of (i) forming S/D openings (notshown) in portions of fin structures 106N-106P that are not underlyingpolysilicon structures 712N-712P, (ii) patterning a masking layer (e.g.,a photoresist layer; not shown) to cover the S/D opening in finstructure 106P, (iii) selectively epitaxially growing a Si layer (notshown) within S/D opening in fin structure 106N, (iv) selectively dopingthe Si layer with n-type dopants (e.g., phosphorus) to form LD and HDn-type layers 109N-110N, as shown in FIGS. 7A and 7C, (v) selectivelyepitaxially growing a SiGe layer (not shown) on HD n-type layer 110N,(vi) selectively doping the SiGe layer with p-type dopants (e.g., boron)to form p-type capping layer 111N, as shown in FIGS. 7A and 7C, (vii)removing the masking layer from the S/D opening in fin structure 106P,(viii) patterning a masking layer to cover S/D region 108N, (ix)selectively epitaxially growing a SiGe layer (not shown) within S/Dopening in fin structure 106P, (x) selectively doping the SiGe layerwith p-type dopants (e.g., boron) to form LD and HD p-type layers109P-110P, as shown in FIGS. 7B and 7D, (xi) selectively epitaxiallygrowing a Si layer (not shown) on HD p-type layer 110P, and (xii)selectively doping the Si layer with n-type dopants (e.g., phosphorus)to form n-type capping layer 111P, as shown in FIGS. 7B and 7D. Afterthe formation of S/D regions 108N-108P, ESL 117 and ILD layer 118A canbe formed to form the structures of FIGS. 7A-7D.

Referring to FIG. 6, in operation 610, polysilicon structures arereplaced with gate structures. For example, as shown in FIGS. 8A-8B,polysilicon structures 712N-712P are replaced with gate structures112N-112P. In some embodiments, gate structures 112N-112P can be etchedback to form gate capping layers 130, as shown in FIGS. 9A-9B. After theformation of gate capping layers 130, ILD layer 118B can be formed toform the structures of FIGS. 9A-9D.

Referring to FIG. 6, in operation 615, first and second contact openingsare formed on the n- and p-type source S/D regions. For example, asshown in FIGS. 10A-10D, first and second contact openings 1020N-1020Pare formed on S/D regions 108N-108P by etching portions of ESL 117 andILD layers 118A-118B on S/D regions 108N-108P.

Referring to FIG. 6, in operation 620, barrier layers are selectivelyformed on sidewalls of the first and second contact openings. Forexample, as described with respect to FIGS. 11A-12D, barrier layers142N-142P are selectively formed on sidewalls of first and secondcontact openings 1020N-1020P. The formation of barrier layers 142N-142Pcan include sequential operations of (i) depositing a nitride layer 142(e.g., SiN) on the structures of FIGS. 10A-10D to form the structures ofFIGS. 11A-11D and (ii) performing an isotropic etch process to removeportions of nitride layer 142 from top surfaces of ILD layer 118A and p-and n-type capping layers 111N-111P to form the structures of FIGS.12A-12D.

Referring to FIG. 6, in operation 625, a pWFM silicide layer isselectively formed on the p-type S/D region. For example, as shown inFIGS. 13A-13D, pWFM silicide layer 131 is selectively formed on S/Dregion 108P. The selective formation of pWFM silicide layer 131 caninclude depositing a pWFM layer 140 on the structures of FIGS. 12A-12D,which can initiate a silicidation reaction between n-type capping layer111P and the bottom portion of pWFM layer 140 (not shown) deposited onn-type capping layer 111N to form the structures of FIGS. 13A-13D. Insome embodiments, pWFM layer 140 can include a work function valuecloser to a valence band-edge energy than a conduction band-edge energyof the material of HD p-type layer 110P of S/D region 108P. For example,pWFM layer 140 can include a metal with a work function value greaterthan 4.5 eV (e.g., about 4.5 eV to about 5.5 eV), which can be closer tothe valence band energy 5.2 eV of Si or 4.8 eV of SiGe than theconduction band energy 4.1 eV of Si or 3.8 eV of SiGe of HD p-type layer110P. In some embodiments, pWFM layer 140 can include Ni, Co, Mn, W, Fe,Rh, Pd, Ru, Pt, Ir, Os, or a combination thereof.

The deposition of pWFM layer 140 can include depositing about 0.5 nm toabout 5 nm thick pWFM layer with a chemical vapor deposition (CVD)process or an atomic layer deposition (ALD) process at a temperatureranging from about 160° C. to about 220° C. and a pressure ranging fromabout 5 Torr to about 10 Torr. In some embodiments, the ALD process caninclude about 300 cycles to about 800 cycles, where one cycle caninclude sequential periods of (i) metal precursor, reactant, and carriergas mixture flow and (ii) a gas purging process for a period of about 3seconds to about 15 seconds. In some embodiments, the reactant gas caninclude ammonia (NH₃), carrier gas can include nitrogen or argon, andpurging gas can include a noble gas.

In some embodiments, the metal precursor can include metal complexes,such as Bis(1,4-di-t-butyl-1,3-diazabutadienyl)M, M(tBuNNCHCtBuO)₂,M(eBuNNCHCiPrO)₂, and M(tBuNNCMeCMeO)₂, where M can be Ni, Co, Mn, W,Fe, Rh, Pd, Ru, Pt, Ir, or Os. As metal complexes have a higher affinityfor Si than SiGe, pWFM layer 140 deposits on n-type capping layer 111P,which includes Si and does not deposit on p-type capping layer 111N,which includes SiGe. The strained lattice structure of SiGe inhibits theadhesion of the metal complexes on p-type capping layer 111N, and as aresult, prevents the formation of pWFM layer 140 on p-type capping layer111N of NFET. Thus, the use of metal complexes as metal precursors forpWFM layer 140 reduces the number of processing steps by eliminating theuse of lithography and etching process for the selective formation ofpWFM silicide layer 131 in PFET 102P, and consequently reduces thedevice manufacturing cost.

In some embodiments, a cleaning process can be performed on thestructures of FIGS. 12A-12D prior to the deposition of pWFM layer 140.The cleaning process can include a fluorine-based dry etching process toremove native oxides from top surfaces of p-type capping layer 111N andn-type capping layer 111P.

In some embodiments, after the formation of pWFM silicide layer 131, theportions of pWFM layer 140 on sidewalls of contact openings 1020N-1020Pcan be removed by a wet etching process to form the structures of FIGS.14A-14D. In some embodiments, the exposed portions of p-type cappinglayer 111N within contact opening 1020N can be selectively removed fromthe NFET structure of FIGS. 13A and 13C or from the NFET structure ofFIGS. 14A and 14C by a wet or dry etching process to form the NFETstructure of FIGS. 16A and 16C.

Referring to FIG. 6, in operation 630, doped nWFM silicide layers areformed on the n-type S/D region and on the pWFM silicide layer. Forexample, as shown in FIGS. 19A-19D, doped nWFM silicide layers 132N and132P are formed on S/D region 108N and on pWFM silicide layer 131,respectively. The formation of doped nWFM silicide layers 132N-132P caninclude sequential operations of (i) performing a cleaning process(e.g., fluorine-based dry etching process) on the structures of FIGS.13A-13D to remove native oxides from top surfaces of p-type cappinglayer 111N and pWFM silicide layer 131, (ii) depositing a dopant sourcelayer 138 on the cleaned structures of FIGS. 13A-13D to form thestructures of FIGS. 17A-17D, and (iii) depositing an nWFM layer 136 onthe structures of FIGS. 17A-17D to form the structures of FIGS. 19A-19D.

During the deposition of nWFM layer 136, the deposition temperature cancause the bottom portions 138 b (shown in FIGS. 17A-17B) of dopantsource layer 138 to thermally decompose and the atoms of the thermallydecomposed bottom portions 138 b to diffuse into the overlying nWFMlayer 136 as dopant atoms. The dopant atoms can induce the formation ofdipole layer 144 and can have concentration profiles 246 or 248 acrosslines E-E and concentration profiles 252 or 254 across lines F-F, asdescribed with reference to FIGS. 2A-2F. The deposition temperature canalso initiate silicidation reactions between (i) the doped bottomportion of nWFM layer 136 (not shown) within contact opening 1020N andp-type capping layer 111N to form nWFM silicide layer 132N, as shown inFIGS. 19A and 19C, and (ii) the doped bottom portion of nWFM layer 136within contact opening 1020P and HD p-type layer 111P through pWFMsilicide layer 131 to form nWFM silicide layer 132P, as shown in FIGS.19B and 19D. In some embodiments, after the deposition of dopant sourcelayer 138, the portions of dopant source layer 138 on the PFET structureof FIGS. 17B and 17D can be selectively removed, as shown in FIGS.18A-18D, to form undoped nWFM silicide layer 132P (not shown) and dopednWFM silicide layer 132N.

In some embodiments, the deposition of dopant source layer 138 caninclude depositing a transition metal, which has an electronegativityvalue smaller than the electronegativity value of the metal of nWFMlayer 136 using a CVD process or an ALD process at a temperature rangingfrom about 300° C. to about 500° C. In some embodiments, dopant sourcelayer 138 can include a transition metal, such as Zr, Hf, Yb, Y, Er, Ce,Sc, and a combination thereof. For effective and complete thermaldecomposition of dopant source layer 138, dopant source layer 138 can bedeposited with a thickness ranging from about 0.05 nm to about 0.5 nm.

In some embodiments, the deposition of nWFM layer 136 can includedepositing a metal with a work function value closer to a conductionband-edge energy than a valence band-edge energy of the material of HDn-type layer 111N of S/D region 108N using a CVD process or an ALDprocess at a temperature ranging from about 300° C. to about 500° C. Forexample, nWFM layer 136 can include a metal with a work function valueless than 4.5 eV (e.g., about 3.5 eV to about 4.4 eV), which can becloser to the conduction band energy 4.1 eV of Si or 3.8 eV of SiGe thanthe valence band energy 5.2 eV of Si or 4.8 eV of SiGe of HD n-typelayer 111N. In some embodiments, nWFM layer 136 can include Ti, Ta, Mo,Zr, Hf, Sc, Y, Ho, Tb, Gd, Lu, Dy, Er, Yb, or a combination thereof.

In some embodiments, the formation of doped nWFM silicide layers132N-132P can include sequential operations of (i) performing a cleaningprocess (e.g., fluorine-based dry etching process) on the structures ofFIGS. 14A-14D, 15A-15D, or 16A-16D, instead of FIGS. 13A-13D, (ii)depositing dopant source layer 138 on the cleaned structures of FIGS.14A-14D, 15A-15D, or 16A-16D, and (iii) depositing nWFM layer 136 ondopant source layer 138. Performing these operations on (i) thestructures of FIGS. 14A-14D can result in the formation of S/D contactstructures 120N-120P (shown in FIGS. 2A-4D) without third liners140N-140P, (ii) the structures of FIGS. 15A-15D can result in theformation of S/D contact structures 120N-120P (shown in FIGS. 5A-5D)without third liners 140N-140P, and (iii) the structures of FIGS.16A-16D can result in the formation of S/D contact structures 120N-120P,as shown in FIGS. 5A-5D.

Referring to FIG. 6, in operation 635, a high temperature annealingprocess is performed. For example, a thermal annealing process can beperformed on the structures of FIGS. 19A-19D in a N₂ ambient at atemperature ranging from about 500° C. to about 800° C. using a rapidthermal annealing (RTA) process, a spike annealing process, or a laserannealing process for a time period ranging from about 100 nanosecondsto about 100 microseconds. After the thermal annealing process, thedopant atoms can have concentration profile 250 across lines E-E (FIGS.19A and 19C) and concentration profile 256 across lines F-F (FIGS. 19Band 19D) if the dopant atoms in nWFM silicide layers 132N-132P include anon-Zr-based transition metal, as described with reference to FIGS.2A-2F. On the other hand, if the dopant atoms include Zr metal, thestructures of FIGS. 20A-20D can be formed with Zr concentration profile358 across lines G-G, as described with reference to FIGS. 3A-3E, afterthe thermal annealing process is performed on the structures of FIGS.19A-19D. The thermal annealing process can improve the quality of nWFMsilicide layers 132N and pWFM silicide layer 131 and interfaces132N-110N and 131-110P, and as a result, reduce contact resistancebetween nWFM silicide layer 132N and S/D region 108N and between pWFMsilicide layer 131 and S/D region 108P.

In some embodiments, a nitride capping layer (not shown) can be formedon the structures of FIGS. 19A-19D after the formation of nWFM silicidelayers 132N-132P and prior to the thermal annealing process. The nitridecapping layer can form nitride capping layers 146N-146P in subsequentprocessing, as shown in FIGS. 4A-4D. The formation of nitride cappinglayer can include depositing a layer of metal, such as Ti or Ta on thestructures of FIGS. 19A-19D and performing a nitridation process usingammonia (NH₃) gas on the layer of metal.

Referring to FIG. 6, in operation 640, contact plugs are formed withinthe first and second contact openings. For example, as shown FIGS.21A-21D, contact plugs 134N-134P are formed within contact openings1020N-1020P. The formation of contact plugs 134N-134P can includefilling contact openings 1020N-1020P in the structures of FIGS. 19A-19Dwith a conductive material and performing a CMP process to form thestructures of FIGS. 21A-21D. The CMP process can substantiallycoplanarize top surfaces of contact structures 120N-120P with the topsurface of ILD layer 118B.

In some embodiments, contact plugs 134N-134P can be formed by fillingcontact openings 1020N-1020P in the structures of FIGS. 20A-20D, insteadof FIGS. 19A-19D, followed by the CMP process to form the structures ofFIGS. 22A-22B. In some embodiments, pWFM layer 140, dopant source layer138, and nWFM layer 136 can be removed from the structures of FIGS.19A-19D prior to filling contact openings 1020N-1020P with theconductive material and performing the CMP process to form thestructures of FIGS. 23A-23D.

The present disclosure provides example semiconductor devices (e.g.,semiconductor device 100) with NFETs (e.g., NFET 102N) and PFETs (e.g.,PFET 102P) having source/drain (S/D) contact structures different fromeach other and provides example methods of forming such NFETs and PFETson the same substrate with reduced contact resistance between S/Dregions and S/D contact structures. The example method forms arrays ofn- and p-type S/D regions on fin structures of NFETs and PFETs. In someembodiments, since the NFET and PFET S/D regions (e.g., S/D regions108N-108P) are formed with respective n- and p-type materials, the NFETand PFET S/D contact structures (e.g., contact structures 120N-120P) areformed with silicide layers different from each other to reduce thecontact resistances between the S/D contact structures and the differentmaterials of the S/D regions.

In some embodiments, the NFET S/D contact structures are formed withnWFM silicide layers (e.g., nWFM silicide layer 132N) that have a workfunction value closer to a conduction band energy than a valence bandenergy of the n-type S/D regions. In contrast, the PFET S/D contactstructures are formed with pWFM silicide layers (e.g., pWFM silicidelayer 131) that have a work function value closer to a valence bandenergy than a conduction band energy of the p-type S/D regions. In someembodiments, dipole layers (e.g., dipole layer 144) can be selectivelyformed at interfaces between the S/D regions and the nWFM silicidelayers of NFETs to further reduce the SBHs between the n-type S/Dregions and the S/D contact structures. The dipole layers can be formedby doping the nWFM silicide layers with metals having electronegativityvalues lower than the metals of the nWFM silicide layers. The metaldopants can induce the formation of dipoles between the metal dopantsand the semiconductor elements of the n-type S/D regions. Such selectiveformation of silicide layers and dipole layers in the semiconductordevices can reduce the contact resistances of the semiconductor devicesby about 50% to about 70% compared to semiconductor devices with thesame NFET and PFET silicide layers and without dipole layers, andconsequently improve the performance of the semiconductor devices.

In some embodiments, a semiconductor device includes a substrate, firstand second fin structures disposed on the substrate, first and secondgate structures disposed on the first and second fin structures,respectively, first and second source/drain (S/D) regions disposedadjacent to the first and second gate structures on the first and secondfin structures, respectively, first and second contact structuresdisposed on the first and second S/D regions, respectively, and a dipolelayer disposed at an interface between the first nWFM silicide layer andthe first S/D region. The first contact structure includes a firstn-type work function metal (nWFM) silicide layer disposed on the firstS/D region and a first contact plug disposed on the first nWFM silicidelayer. The second contact structure includes a p-type work functionmetal (pWFM) silicide layer disposed on the second S/D region, a secondnWFM silicide layer disposed on the pWFM silicide layer, and a secondcontact plug disposed on the pWFM silicide layer.

In some embodiments, a semiconductor device includes first and secondgate structures disposed on first and second fin structures,respectively, an n-type source/drain (S/D) region and a p-type S/Dregion disposed on the first fin structure and the second fin structure,respectively, first and second contact structures disposed on the n-typeand p-type S/D regions, respectively, and a dipole layer disposed at aninterface between the ternary compound layer and the n-type S/D region.The first contact structure includes a ternary compound layer disposedon the n-type S/D region, a first n-type work function metal (nWFM)silicide layer disposed on the ternary compound layer, and a firstcontact plug disposed on the first nWFM silicide layer. The secondcontact structure includes a p-type work function metal (pWFM) silicidelayer disposed on the second S/D regions, a second nWFM silicide layerdisposed on the pWFM silicide layer, and a second contact plug disposedon the pWFM silicide layer.

In some embodiments, a method includes forming first and second finstructures on a substrate, forming first and second source/drain (S/D)regions on the first and second fin structures, respectively, formingfirst and second contact openings on the first and second S/D regions,respectively, selectively forming a p-type work function metal (pWFM)silicide layer on the second S/D region, forming a doped n-type workfunction metal (nWFM) silicide layer on the pWFM silicide layer and onthe first S/D region, forming a ternary compound layer between the dopednWFM silicide layer and the first S/D region, and forming first andsecond contact plugs within the first and second contact openings.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a substrate;first and second fin structures disposed on the substrate; first andsecond gate structures disposed on the first and second fin structures,respectively; first and second source/drain (S/D) regions disposedadjacent to the first and second gate structures on the first and secondfin structures, respectively; first and second contact structuresdisposed on the first and second S/D regions, respectively, wherein thefirst contact structure comprises a first n-type work function metal(nWFM) silicide layer disposed on the first S/D region and a firstcontact plug disposed on the first nWFM silicide layer, and wherein thesecond contact structure comprises a p-type work function metal (pWFM)silicide layer disposed on the second S/D region, a second nWFM silicidelayer disposed on the pWFM silicide layer, and a second contact plugdisposed on the pWFM silicide layer; and a dipole layer disposed at aninterface between the first nWFM silicide layer and the first S/Dregion.
 2. The semiconductor device of claim 1, wherein the dipole layercomprises a dopant atom of the first nWFM silicide layer and asemiconductor atom of the first S/D region.
 3. The semiconductor deviceof claim 1, wherein the first nWFM silicide layer comprises dopants of atransition metal, and wherein the dopants have a concentration profilewith a peak concentration at the interface between the first nWFMsilicide layer and the first S/D region.
 4. The semiconductor device ofclaim 1, wherein the first nWFM silicide layer comprises metal dopantswith an electronegativity value smaller than an electronegativity valueof a metal in a metal silicide of the first nWFM silicide layer.
 5. Thesemiconductor device of claim 1, wherein the first and second nWFMsilicide layers are doped with a transition metal.
 6. The semiconductordevice of claim 1, wherein the first nWFM silicide layer is doped with atransition metal and the second nWFM silicide layer is undoped.
 7. Thesemiconductor device of claim 1, wherein the first and second contactstructures further comprise first and second liners along sidewalls ofthe first and second contact plugs, respectively, and wherein the firstand second liners comprise a metal or an oxide of a metal of the dipolelayer.
 8. The semiconductor device of claim 1, wherein the first andsecond contact structures further comprise first and second liners alongsidewalls of the first and second contact plugs, respectively, andwherein the first and second liners comprise a metal or an oxide of ametal of the first nWFM silicide layer.
 9. The semiconductor device ofclaim 1, wherein the first and second contact structures furthercomprise first and second liners along sidewalls of the first and secondcontact plugs, respectively, and wherein the first and second linerscomprise a metal or an oxide of a metal of the pWFM silicide layer. 10.The semiconductor device of claim 1, wherein the first and secondcontact structures further comprise first and second capping layersdisposed on the first and second nWFM silicide layers, respectively. 11.A semiconductor device, comprising: first and second gate structuresdisposed on first and second fin structures, respectively; an n-typesource/drain (S/D) region and a p-type S/D region disposed on the firstfin structure and the second fin structure, respectively; first andsecond contact structures disposed on the n-type and p-type S/D regions,respectively, wherein the first contact structure comprises a ternarycompound layer disposed on the n-type S/D region, a first n-type workfunction metal (nWFM) silicide layer disposed on the ternary compoundlayer, and a first contact plug disposed on the first nWFM silicidelayer, and wherein the second contact structure comprises a p-type workfunction metal (pWFM) silicide layer disposed on the p-type S/D regions,a second nWFM silicide layer disposed on the pWFM silicide layer, and asecond contact plug disposed on the pWFM silicide layer; and a dipolelayer disposed at an interface between the ternary compound layer andthe n-type S/D region.
 12. The semiconductor device of claim 11, whereinthe ternary compound layer comprises a zirconium-based ternary compound.13. The semiconductor device of claim 11, wherein the dipole layercomprises a metal atom of the ternary compound layer and a semiconductoratom of the n-type S/D region.
 14. The semiconductor device of claim 11,wherein the first and second nWFM silicide layers are doped with atransition metal.
 15. The semiconductor device of claim 11, wherein thefirst nWFM silicide layer is doped with a transition metal and thesecond nWFM silicide layer is undoped.
 16. The semiconductor device ofclaim 11, wherein the first and second contact structures furthercomprise first and second liners along sidewalls of the first and secondcontact plugs, respectively, and wherein the first and second linerscomprise a metal of the dipole layer, the pWFM silicide layer, or thefirst nWFM silicide layer.
 17. A method, comprising: forming first andsecond fin structures on a substrate; forming first and secondsource/drain (S/D) regions on the first and second fin structures,respectively; forming first and second contact openings on the first andsecond S/D regions, respectively; selectively forming a p-type workfunction metal (pWFM) silicide layer on the second S/D region; forming adoped n-type work function metal (nWFM) silicide layer on the pWFMsilicide layer and on the first S/D region; forming a ternary compoundlayer between the doped nWFM silicide layer and the first S/D region;and forming first and second contact plugs within the first and secondcontact openings.
 18. The method of claim 17, wherein the forming thedoped nWFM silicide layer comprises depositing a dopant source layer onthe first S/D region and on the pWFM silicide layer, and wherein thedopant source layer comprises a metal with an electronegativity valuesmaller than an electronegativity value of a metal in a metal silicideof the doped nWFM silicide layer.
 19. The method of claim 17, whereinthe forming the ternary compound layer comprises: depositing azirconium-based dopant source layer on the first S/D region and on thepWFM silicide layer; depositing an nWFM layer on the dopant sourcelayer; and performing an annealing process.
 20. The method of claim 17,further comprising depositing a nitride capping layer on the doped nWFMsilicide layer.